1. Field of the Invention
The present invention relates to an improvement in the process for the manufacture of beta-methylthiopropionaldehyde (hereinafter referred to as MTPA) from methylmercaptan and an acrolein containing off-gass originating from the catalytic oxidation of propylene.
2. Description of the Prior Art
It is known to prepare MTPA from methylmercaptan and a gas mixture containing acrolein, which has been obtained by catalytic oxidation of propylene. For example, Netherlands Patent Application No. 68/09,647 describes a process whereby MTPA is obtained in the liquid state in a reaction zone, by absorption of a gas mixture containing acrolein, by the MTPA, and reaction of the acrolein dissolved in the MTPA with methylmercaptan. According to this process, it is also possible to first bring the methylmercaptan into contact with the MTPA in a reaction zone, and then contact the mixture thus obtained with a gas containing the acrolein. In these two variants, the formation of the MTPA is conducted in the presence of an aqueous solution at a pH of between 4 and 7, and the MTPA is recirculated into the reaction zone. However, it is thus necessary to carry out a supplementary stage of an extraction treatment of the aqueous phase of the liquid product obtained to obtain a total yield of MTPA of about 91%. On a commercial scale, the mandatory extraction step in this and other similar processes obviously increases the cost of production while complicating the overall method. Accordingly, the need exists to simply, yet highly efficiently and economically, produce MTPA from methylmercaptan and an acrolein-containing gas.